The multiplication or reproduction of [[endothelial cell]]s, resulting in the expansion of a cell population.
----

In response to angiogenic stimuli, endothelial cells (ECs) proliferate, migrate, and coalesce to form primitive vascular labyrinths that undergo maturation and remodeling, accompanied by recruitment of smooth muscle cells to give rise to mature blood vessels.
----
see [[Gorham-Stout disease]].